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| seasickness |
Motion sickness is a form of vertigo in which autonomic symptoms predominate.
Causes
The cause is thought to be disturbance of the vestibular apparatus of the inner
ear, which controls balance, brought on by unaccustomed types of movement.
During travel conflicting stimuli are received in the brain from the eyes
and remembered experience of usual forms of movement, such as walking.
This sensory mismatch is interpreted as a noxious stimulus and initiates a
physiological response similar to that to substances perceived as poisonous,
and a number of autonomic nervous system responses are activated to reject the
perceived poison.
The body adapts to unfamiliar types of motion on prolonged or repeated
exposure, explaining why seasickness, for example, tends to subside after a few
days.
Signs and symptoms
Muscarinic effects, including:
– nausea
– vomiting
– increased salivation
– general malaise
– pallor
– sweating
– yawning
– hyperventilation.
Gastric motility is also reduced and digestion impaired.
Treatment
Sedating antihistamines and hyoscine are licensed for use without prescription
for prophylaxis and treatment of motion sickness. They appear to be of more or
less equivalent efficacy.
They are effective for prevention, but use for treatment is often unsuccessful as
vomiting and gastric stasis prevent or substantially reduce their absorption.
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